Payroll integration with Project

Scenario:
I have a resource of an employee working on a project. To allocate payroll cost to project, I have different scenarios:
1- Use monthly fixed salary of 400$ as cost for the project, ensuring no double expense is booked at organization level (Payroll management system and project costing)
2- In PMS employee is paid 10$/hr. For the project he will be paid 15$ (extra 5$).

Also, for defining transaction source as payroll should i also define accounting methods and rules?